1. Field
The disclosed concept pertains generally to electrical switching apparatus and, more particularly, to, for example, circuit breakers. The disclosed concept further pertains to operating mechanisms for opening separable contacts. The disclosed concept still further pertains to cams, such as for example, for a coupling mechanism of an operating mechanism.
2. Background Information
Medium voltage circuit breakers include, for example and without limitation, a plurality of separable contacts coupled to an operating mechanism having a common spring-operated closing and tripping device. The operating mechanism includes one or more opening springs which separate the contacts and a pair of closing springs which close the contacts as well as charge the opening spring(s). The separable contacts are closed by releasing the energy stored in the closing springs through activation of a closing trigger mechanism. This can be done manually or remotely through a solenoid. The closing springs are charged manually by a lever arm through a ratchet coupling, or, more preferably, by a motor. An electronic trip circuit monitors the load currents and actuates an opening trigger mechanism through an opening solenoid if a load current exceeds certain current-time characteristics.
As shown in FIGS. 1 and 2, a switch gear apparatus 10 includes a cabinet or enclosure 13 for enclosing a circuit breaker 15. The example circuit breaker 15 is, preferably, a draw-out three-phase vacuum circuit interrupter having controls on a front panel 17 for manually operating the circuit breaker 15. The circuit breaker 15 has wheels 19 which engage rails 21 for inserting the circuit breaker 15 into and removing the circuit breaker 15 from the enclosure 13. The enclosure 13 includes at least one line terminal 27 and at least one load terminal 29. The circuit breaker 15 includes at least one line terminal 23 and at least one load terminal 25. Typically, the switch gear apparatus 10 has three circuit breaker line and load terminals 23, 25 and three corresponding enclosure line and load terminals 27, 29. The circuit breaker line and load terminals 23, 25 are positioned to engage, and be electrically coupled to, the enclosure line and load terminals 27, 29. Movement of the circuit breaker 15 along the rails 21 also effects connection and disconnection of the circuit breaker line and load terminals 23, 25 with the enclosure line and load terminals 27, 29. While a medium voltage vacuum interrupter is shown for the circuit breaker 15, the disclosed concept is also applicable for use with air circuit breakers.
Referring to FIGS. 3A-3C, fixed on a crank shaft 85 (also shown in FIG. 2) between supports 87, 89 (FIG. 2) is a closing cam 91, which includes a notch 93 in a peripheral cam surface thereof. A main link roller 133 engages the peripheral cam surface of the closing cam 91 which, as the crank shaft 85 rotates, pushes on main links 129 (only one link is shown) to rotate a pole shaft 55 through the eccentricity in the closing cam 91 peripheral cam surface. A trip latch reset spring 159 biases the main link roller 133 against the peripheral cam surface of the closing cam 91 until it falls into the notch 93 with the closing springs 69, 71 (FIG. 2) latched in the charged condition. This permits the trip latch reset spring 159 to rotate a hatchet 139 counter-clockwise (with respect to FIGS. 3A-3C) to the latched position in which a latch edge 145 is engaged by a D-shaft 149 as shown in FIGS. 3B and 3C. When a closing spring release (not shown) is actuated, the closing springs 69, 71 rapidly rotate the crank shaft 85. The increasing effective diameter of the closing cam 91 produced by the eccentricity of the cam 91 surface, pushes the main links 129 downward (with respect to FIG. 3B) and to the position shown in FIG. 3C. This rotates the pole shaft 55 in a counterclockwise direction (with respect to FIG. 3C) to drive a push rod 51 to the left (with respect to FIG. 3C) to close separable contacts 40 (FIG. 1) while, as can be seen in FIG. 3C, the hatchet 139 remains engaged by the D-shaft 149.
As a relatively high latch load force is rotated around the cam 91, the affect on the cam material changes with the thickness (as measured in the plane of FIGS. 3A-3C) of the cam 91. At the thinnest point, which is proximate the notch 93, the cam 91 may have insufficient strength to withstand the load. The cam 91 shown in FIG. 2 includes four laminations.
There is room for improvement in cams.
There is also room for improvement in operating mechanisms.
There is further room for improvement in electrical switching apparatus, such as circuit breakers.